title: Comparison of expansive pedicle screw and polymethylmethacrylate-augmented pedicle screw in osteoporotic sheep lumbar vertebrae: biomechanical and interfacial evaluations.
abstract: BACKGROUND
  It was reported that expansive pedicle screw (EPS) and polymethylmethacrylate-augmented pedicle screw (PMMA-PS) could be used to increase screw stability in osteoporosis. However, there are no studies comparing the two kinds of screws in vivo. Thus, we aimed to compare biomechanical and interfacial performances of EPS and PMMA-PS in osteoporotic sheep spine.
  
  
  RESULTS
  After successful induction of osteoporotic sheep, lumbar vertebrae in each sheep were randomly divided into three groups. The conventional pedicle screw (CPS) was inserted directly into vertebrae in CPS group; PMMA was injected prior to insertion of CPS in PMMA-PS group; and the EPS was inserted in EPS group. Sheep were killed and biomechanical tests, micro-CT analysis and histological observation were performed at both 6 and 12 weeks post-operation. At 6-week and 12-week, screw stabilities in EPS and PMMA-PS groups were significantly higher than that in CPS group, but there were no significant differences between EPS and PMMA-PS groups at two study periods. The screw stability in EPS group at 12-week was significantly higher than that at 6-week. The bone trabeculae around the expanding anterior part of EPS were more and denser than that in CPS group at 6-week and 12-week. PMMA was found without any degradation and absorption forming non-biological "screw-PMMA-bone" interface in PMMA-PS group, however, more and more bone trabeculae surrounded anterior part of EPS improving local bone quality and formed biological "screw-bone" interface.
  
  
  CONCLUSIONS
  EPS can markedly enhance screw stability with a similar effect to the traditional method of screw augmentation with PMMA in initial surgery in osteoporosis. EPS can form better biological interface between screw and bone than PMMA-PS. In addition, EPS have no risk of thermal injury, leakage and compression caused by PMMA. We propose EPS has a great application potential in augmentation of screw stability in osteoporosis in clinic.
authors.affiliation: Department of Orthopaedics, General Hospital of Chengdu Military Region, Chengdu, Sichuan Province, P.R.China.
authors.forename: Da
authors.initials: D
authors.lastname: Liu
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.forename: Bo
authors.initials: B
authors.lastname: Zhang
authors.forename: Qing-yun
authors.initials: QY
authors.lastname: Xie
authors.forename: Cai-ru
authors.initials: CR
authors.lastname: Wang
authors.forename: Jin-biao
authors.initials: JB
authors.lastname: Liu
authors.forename: Dong-fa
authors.initials: DF
authors.lastname: Liao
authors.forename: Kai
authors.initials: K
authors.lastname: Jiang
authors.forename: Wei
authors.initials: W
authors.lastname: Lei
authors.forename: Xian-ming
authors.initials: XM
authors.lastname: Pan
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D015519:Bone Density; D001863:Bone Screws; D005260:Female; D021621:Imaging, Three-Dimensional; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology* / Q000601:surgery*; D010024:Osteoporosis / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology* / Q000601:surgery*; D019904:Polymethyl Methacrylate / Q000737:chemistry*; D012756:Sheep; D016474:Weight-Bearing; D055114:X-Ray Microtomography
chemical_list: D019904:Polymethyl Methacrylate